Add some string operations

std/string/array/dup.lb

@@ -0,0 +1,2 @@
+@ 0
+ args 0

std/string/array/rev.lb

@@ -0,0 +1,2 @@
+args 0
+size

std/string/null/rev.lb

@@ -0,0 +1,12 @@
+@ 0
+ args 1
+ kjz 1
+ jmp 0
+
+@ 1
+ pop
+ size
+ #exec std/rev.lb
+ push 0
+ size
+ #exec std/rev.lb